The Search network is made up of users actively looking (i.e. searching) for goods, services, and information. This express intent by the user means that your search ads are focused on informing the user about your options so the user can take action.
The Display network is made of up publisher sites that show ads. The user's primary purpose on that page is to watch a video or read an article. Your ad needs to draw attention to itself so the user wants to interact with your ad and visit your site.
As the user intent and the networks are so different from each other, it's best to run your ads only on search or only on the display network and not combine the two.
When you have a campaign running on both networks, you will see an alert on the dashboard listing these campaigns.
To change the settings and only run the campaign on the Search Network, select the campaign(s) by clicking in the checkbox next to the name and clicking on the button "Run on only Search Network".